1. Field of the Invention
The present invention relates to a method of diffusing zinc into an article having a surface of III-V compound semiconductor containing phosphorus as a group V constituent element, and a method of heating an article having a surface of III-V compound semiconductor containing phosphorus as a group V constituent element.
2. Related Background Art
In manufacturing a semiconductor device on an InP substrate, steps of heating the InP substrate are carried out, such as a step of diffusing zinc into the InP substrate and a step of annealing the InP substrate after implanting ions into the InP substrate. In these heating steps, the InP substrate is heated to a high temperature of, for example, about 550 degrees centigrade. When the InP substrate is heated at such a high temperature, InP in a surface of the InP substrate is thermally decomposed into indium and phosphorus individually. A large part of the phosphorus is sublimed into the vapor phase because vapor pressure of phosphorus is higher than that of indium. So-called phosphorus loss phenomenon occurs in the surface of the InP substrate. When the loss of phosphorus occurs, a number of defects are generated in the surface of the InP substrate.
The loss of phosphorus occurs not only in the InP substrate but also in a GaP substrate, and furthermore, the loss of phosphorus occurs in a semiconductor film such as GaxIn1-xP (0 less than x less than 1) grown on a GaAs substrate.
Japanese Patent Laid-Open No. 2000-49105 publication, for example, discloses a method of preventing the loss of phosphorus. In the method disclosed in the publication, a non-doped InP substrate having a surface roughened (hereinafter, referred as to a dummy substrate) is prepared. The dummy substrate is disposed such that the roughened surface faces the surface of the InP substrate. Thereafter, the InP substrate and the dummy substrate are heated. During the heating, phosphorus is sublimed from the dummy substrate to form phosphorus vapor, and the surface of the InP substrate is exposed to the phosphorus vapor at a predetermined vapor pressure. The phosphorus vapor serves to prevent the loss of phosphorus in the InP substrate.
However, the method as described above cannot be available as the InP substrate increases in diameter. The diameter of the dummy substrate need to be larger than that of the InP substrate because the entire surface of the InP substrate should be exposed to a phosphorus vapor. If an InP substrate having the diameter of four inches, which is widely used at present, is heated by use of the method, the diameter of a dummy substrate should be more than 4 inches. But, it is not easy to obtain a dummy substrate of a diameter more than 4 inches. The dummy substrate of four-inch diameter is expensive, if obtained, and thus the use of the expensive dummy substrate increases costs required for steps of heating the InP substrate.
In light of such a matter, the inventors have examined a method of heating the InP substrate without using the dummy substrate and have thereby attained the present invention.
It is an object of the present invention to provide a method of diffusing zinc into an article having a surface of III-V compound semiconductor containing phosphorus as a group V constituent element, without loss of phosphorus from the surface thereof, and to provide a method of diffusing zinc into the article.
One aspect of the present invention is a method of diffusing zinc into an article having a surface of a III-V compound semiconductor containing phosphorus as a group V constituent element. The method includes the steps of: (a) providing the article, an alloy, and a material source containing zinc and phosphorus in a heating furnace, the alloy including tin, indium and phosphorus as main constituents; (b) increasing a temperature of the article in an atmosphere containing vapor of phosphorus supplied from the alloy; and (c) exposing a surface of the article in an atmosphere containing vapor of zinc and phosphorus from the material source to diffuse zinc into the article.
In the method, the alloy may be produced from a combination of a tin material and an indium material, and one material of an indium phosphorus material and a phosphorus material. The combined material is prepared in a molar ratio of indium to tin of 0.65 or more but not exceeding 1.3.
In the providing step, the alloy is provided in a first container having a bottom portion. The first container is provided in the heating furnace such that the bottom portion of the first container faces a surface of the article. The bottom portion has a plurality of through holes therein. The material is provided in a second container. The second container is provided in the heating furnace. The second container may be provided adjacent to the first container. The second container includes an opening in a bottom portion thereof. In the heating step, the first container is provided such that the bottom portion faces the article. In the diffusing step, the second container is provided on the article.
Preferably, after the diffusing step, the method further includes the step of lowering temperature of the article in vapor of phosphorus produced from the alloy. This step prevents the loss of phosphorus in decreasing the temperature of the article.
Preferably, in the step of lowering the temperature as described above, the first container is provided such that the bottom portion of the first container faces the article. In this step, the surface of the article can be surely exposed to the vapor of phosphorus in decreasing the temperature of the article.
Preferably, in preparing the alloy, the tin material, the indium material, and any one of the indium phosphorus material and the phosphorus material is prepared to heat them at a temperature equal to or higher than a temperature at which the article is to be processed. After this preparation, the phosphorus concentration can be saturated in the alloy when the alloy is heated and the vapor of phosphorus is generated from the alloy.
Furthermore, it is preferable to contain the alloy including solid indium phosphorus or solid phosphorus when the surface of the article is exposed to the vapor of phosphorus generated from the alloy. When this alloy is used, the phosphorus concentration is saturated in the alloy.
Another aspect of the present invention is a method of heating an article having a surface of a III-V compound semiconductor containing phosphorus as a group V constituent element, the method comprising the steps of: (a) providing an alloy in a heating furnace, the alloy including tin, indium, and phosphorus as main constituents; and (b) raising a temperature of the article in an atmosphere containing vapor of phosphorus supplied from the alloy.
In this method, the alloy may be prepared from a combination of a tin material and an indium material and any one material of an indium phosphorus material and a phosphorus material. The combined material has a molar ratio of indium to tin of 0.65 or more but not exceeding 1.3.
Preferably, after the raising step, the heating method further includes the step of exposing the surface to the vapor of phosphorus produced from the alloy for a predetermined period of time while heating the article. This method prevents the loss of phosphorus in the article during the heating of the article for the predetermined time.
Preferably, after the exposing step, the heating method further includes the step of lowering temperature of the semiconductor substrate while exposing the surface of the article to the vapor of phosphorus produced from the alloy. This method prevents phosphorus atoms in the article from subliming in lowering the temperature of the article.
Preferably, in the providing step, the alloy is prepared in a container, provided in the heating furnace, having a bottom portion. The container is provided in heating furnace such that the bottom portion faces the surface of the article. The container has a plurality of through holes in the bottom portion. It is preferable that the bottom portion of the container faces the surface of the article in exposing the surface of the article to the vapor of phosphorus generated from the alloy. The loss of phosphorus from the article can be prevented.
Preferably, in preparing the alloy, the tin material, the indium material, and any one of the indium phosphorus material and the phosphorus material is heated at a temperature equal to or higher than that at which the article is to be heated. Moreover, the alloy contains any one material of a solid indium phosphorus material and a solid phosphorus material in exposing the surface to the vapor of phosphorus generated from the alloy.